[Bugfix] Ensure JSON encoding preserves non-ASCII characters in Llama3JsonToolParser

[PedroF43]

This PR fixes an issue where streaming tool arguments containing non-ASCII characters (e.g., ã, à) were being escaped into their Unicode sequences (e.g., \u00e1). This behavior not only altered the intended format but also caused the arguments to be duplicated at the end of the stream—first as escaped sequences and then as their proper non-escaped versions. The fix ensures that all JSON serialization for tool arguments consistently uses ensure_ascii=False, preserving the original non-ASCII characters and preventing any duplication.

[github-actions]

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[DarkLight1337]

cc @K-Mistele

[maxdebayser]

Nice! Can you add a unit test for this?

[mgoin]

Superseded by #17704